Variable sound absorption systems

 

If you are working on a building project with a large space, you might want to use it for a broad range of activities.

Depending on the building is, the activities could be:

  • amplified music performances
  • quiet acoustic music performances
  • loud acoustic music performances
  • drama performances
  • conferences or lectures
  • sports events
  • exams
  • fairs
  • and more.

The space will not only need to be very flexible physically to accommodate these activities, but also acoustically. In fact, each activity requires very different sound reverberation conditions to work optimally and ensure acoustic comfort for the users (and listeners for some cases).

 

Note: If you need a refresher on the basics of sound reverberation, go to this page.

 

One of the ways to make a space acoustically flexible is by changing the sound absorption in the space. Essentially, you either:

  • reveal or add sound absorptive materials to make the room less reverberant, and;
  • hide or take away sound absorptive materials to make the room more reverberant (or more lively).

This is done with systems called variable acoustic systems or also variable sound absorption systems.

 

  Note: Other ways of changing the sound reverberation in spaces is by changing their volume or artificially adding reverberation with electroacoustic systems.

What are these systems? This post presents, with pros and cons explained, some of the most commonly used variable sound absorption systems, including:

 

Note: the following documents have been helpful to write this post:

  • Auditorium Acoustics and Architectural Design – Mike Barron;

  • Acoustic Absorbers and Diffusers: Theory, Design and Application (Third Edition) – Trevor Cox and Peter d’Antonio

  • Sound Materials: A Compendium of Sound Absorbing Materials for Architecture and Design – Tyler Adams

 

Acoustic Curtains/Drapes


Acoustic curtains can be either:

  • extended along walls to lower the sound reverberation in a space, or;
  • stored in corners or in dedicated cupboards to increase the sound reverberation.

To know more on acoustic curtains (such as installation, acoustic performance, characteristics of the fabric, etc), follow this link to the Acoustic Design Catalogue.

Variable sound absorption with curtains (left: extended - right: stored) - variable acoustics - acoustic curtains - acoustic drapes - performing arts
Variable sound absorption with curtains (left: extended – right: stored)

 

Pros

 

Acoustic curtains drapes - relatively cheap  Relatively cheap

Acoustic curtain systems mostly involve fabric and a rail, which is relatively inexpensive compared to other sound absorption materials or systems.

 

acoustic curtains drapes - easy to deploy   

Easy to operate

They are also manually operated. No need for a complicated motorised system.

 

    Quick to deploy

Unlike certain systems that take a few minutes to deploy (or even longer), deploying acoustic curtains only takes a few seconds.

 Cons

 

Acoustic curtains - fullness - sound absorption limited  Limited sound absorption

Curtains are not the most efficient sound absorber. Consequently, you need more material to cover large wall surfaces and provide a sufficient variation in the reverberation time. If you design a space with a large volume, you could also struggle to find enough available space.

 

Absorb sound at mid and high frequencies - sound absorption  Absorb sound at mid and high frequencies

As a fibrous material, fabric is more efficient at absorbing sound at mid and high frequencies than at low frequencies.

Therefore, you will need to find other sound absorption means if you want to control the sound reverberation at low frequencies (especially in spaces where music is played). 

Jonathan Berman - Peter Serkin - Tanglewood

 

Interview with Jonathan Berman – Part 2: Sounds and acoustics

 

MF: Do you also work on the positioning of the instruments depending on the hall?

JB: Absolutely – for me it’s an incredibly important aspect, not just for the quality of sound and comfort of playing but also as a means of expression. Orchestras have, throughout the ages, been set up in many different ways, depending on the repertoire, the time period, the concert hall and for me it is definitely part of the expressive role of a conductor to be flexible with orchestral seating.

Just to begin with, there are many pieces (particularly written in the last 60 years or so) where the composer asks for specific or unusual seating plans of orchestras because the roles played by certain instruments or groups of instruments do not function in the traditional manner.

The most famous extreme example of this would be Stockhausen’ Gruppen where he asks for three separate orchestras to surround the audience creating the most astonishing surround sound effects.

Stockhausen Gruppen - Jonathan Berman
Stockhausen Gruppen with three orchestras surrounding the audience

But there are many examples of pieces placed on stage with different layouts. From Stockhausen’s Fünf weitere Sternzeichen where the strings are placed behind the winds, brasses, harps and percussion and space is left between the conductor and the audience for a solo tuba to move around. Or Boulez’s Rituel where 8 groups of players are asked to be as far away from each other as possible on stage (perhaps an early form of social distancing!).

For more traditional repertoire there are some decisions you have to make, for instance where to place your violins. In most music before around 1825(ish), Beethoven, Mozart and Haydn for example, you probably want the 1st violins on the conductor’s left hand side and the 2nd violins on the right hand side, so that the audience will experience a stereo, antiphonal effect as the composers often write dialogues between the violins into their music. 

Jonathan Berman - Orchestra layout with violins on each side
Orchestra layout with 1st violins on the left side and the 2nd violins on the right side

Whereas for some composers like maybe Mahler, Tchaikovsky, Strauss and some more modern composers, you have all violins sitting on the same side so that the sound image comes from the same place and arrives already mixed to the audience. 

There is also a question in every concert about the double basses. Personally, I love big bass sounds and I want the audience to really hear them as the foundation of the music.

I love having bases along the back of an orchestra, as opposed to one side, so that the sound of the lowest note in the orchestra permeates through the orchestra and the whole sound (and intonation) of the orchestra is based on the bases (pun intended). Although of course, it depends on the acoustic properties of the venue and what sounds best.

However, there is some music for which the music written by the composer demands different orchestral textures and timbres. A great example is Stravinsky’s music for which you would place your bass section to one side so that the bass sonorities are clear and more separated from other instruments in the orchestra to best serve the way the music functions.

And then, of course, the complication is that you are not playing in venues that are all the same or with robots but real people. If you want the music in a certain way for the audience, you need to create conditions for the musicians to play to their best. The setting up of the orchestra also becomes a dialogue between your ideals, the venue and the players.

For the recording of the Symphony No. 1 from Franz Schmidt, I really wanted antiphonal violins, because I love that stereo sound and I felt there were a number of passages in the music where that would really add something. However, when we got into the sessions, the violins didn’t feel comfortable being so far away from each other (in the recording studio they struggled to hear each other from opposite ends of the stage). Because there are many passages with a lot of delicate details that they had to really get together as a singular violin section, the leader advised me to put them all on one side, which I did.

Jonathan berman - Orchestra layout for the recording of the Symphony No. 1 from Franz Schmidt
Orchestra layout for the recording of the Symphony No. 1 from Franz Schmidt

Suddenly they played with such confidence as they could all hear each other that it simply sounded so much better and outweighed my initial ideas. (This also shows the value of listening to what the players have to say – especially when they know their own orchestras and venues much better than you do!)

MF: Part of the design of stages is to control the loudness on stage, so the music is not too loud and you manage the noise exposure of the musicians. What are your views and experience on this?

JB: Well this is a very important issue, particularly at the moment. Modern orchestras accept (and even expect) the wearing of earplugs and sound protectors on stage as a normality. They are necessary to protect musicians who are seriously struggling with hearing loss after years of playing in orchestras – and even more in opera pits.

However, it is undeniable that the volume of orchestras has increased over the years. For a number of reasons – the halls we play in are often much bigger, the instruments have changed as well, all of which has developed symbiotically with a changing aesthetics of orchestral and instrumental sound.

In older halls like the Musikverein, you notice how loud a modern orchestra can sound. Whereas if you play in Chicago Symphony Centre, in The Shed in Tanglewood or the Royal Albert Hall, suddenly you have to develop this sound which projects and travels over huge distances.

The Shed - Tanglewood - Jonathan Berman
The Shed, Tanglewood

For me, I have actually learned a lot from this phenomenon. The orchestras whose sound I love (Vienna Philharmonic, Cleveland Orchestra, the Philadelphia Orchestra, Paris Conservatoire Orchestra, Czech Philharmonic, Concertgebouw Orchestra or Berlin Konzerthaus Orchestra) all play (or played) in smaller, old fashioned halls where making music isn’t about projecting your sound to the back of the 5000 seater hall, but more about creating warmth. Practically you don’t need to play too loudly in order for everyone just to hear, and so what you can do is discover more colours and nuances in the sound colours.

This idea has been central to my ideal of orchestral sound and, whilst both conducting and rehearsing, I often find myself asking orchestras to play softer, focusing on tone quality and warmth more than projection.

MF: What is your view on the quality of different styles of halls? Especially between shoebox and vineyard styles.

Yes, very interesting question. The first thing is that all musics are different. And I don’t just mean classical, pop, etc, I also mean Bach, Mozart, Haydn, Stravinsky, Boulez, etc. There is no absolute ‘perfect’ acoustic where you can play all music equally effectively. So even the idea that one style of hall is better acoustically and the other style better visually is not true (for me) because it depends on the repertoire being performed.

I have to say that I have experienced phenomenal concerts in both styles of hall and enjoyed performing in both, but I think the audience perspective is more important – at least it has to take into account the orchestra’s perspective because they are highly unlikely to perform a great concert if they are not comfortable on stage.

I love the social ideal in a vineyard hall (think Berlin Philharmonie, the New World Centre Miami, or the Leipzig Gewandhaus from the 1980s) that the audience is closer to the stage, they have better visual contact, and the hall doesn’t dissect communities by separating the expensive seats from the cheap seats.

New world symphony - miami
New World Symphony, Miami

However, I sat in many different seats in shoebox concert halls and felt incredibly connected to the stage – particularly when the halls aren’t too big (Concertgebouw, Musikverein, Snape Maltings or Berlin Konzerthaus).

Interesting to note that in the old style halls, the most expensive seats are normally at the front of the balcony which are the furthest from the stage, but of course still close enough to feel very connected.

I do think that we shouldn’t forget that music is an auditory art form. Whilst there are many ways to enjoy concerts, for social reasons, meditating on your day, enjoying the visual drama of the playing of the instruments, or just having a nice nap. But it is when somebody listens to the music actively that a live concert becomes something unique and nothing else in the world comes close. This is the experience we should all be striving for people to have.

MF: Can you share a little more about your favourite venues? There may be some you would advise people to go to or you have some interesting tips about some types of venues.

One of the cleverest halls is the Seiji Ozawa Hall in Tanglewood. It was completed in the 90s and in essence, it is a very traditional and fairly small shoebox with balconies. There is a summer festival there where the Boston Symphony Orchestra goes. The back wall of the hall can be folded out and opens to this sort of amphitheatre of a grass hill where people come, have picnic and listen to music all weekend. It is an amazing place. 

 

Seiji Ozawa Hall - Tanglewood - Jonatha Berman
Seiji Ozawa Hall, Tanglewood

It really has both the inside and the outside atmospheres. You get this wonderful, warm acoustic, and actually, over the six or seven years of conducting concerts there, the increase of moisture in the wood seems to have improved the warmth of the hall.

I think Suntory Hall in Tokyo is one of the most extraordinary halls. There is something magical about the sound there. The sound feels like you are not only close to the stage, but somehow you are also right at the back of the hall.  Music sounds there as one single sound, it has this sort of visceral attack, very clean, very clear. You hear all the details and also the resonance of the space.

Opera houses also are very interesting. They are often quite dry. You have this small box in which the orchestra plays (the orchestra pit), and the sound goes vertically up from this pit, which the audience then hears mostly as reflected sound. You have singers on stage, who sing directly at the audience and the orchestra (allowing both to hear the singers clearly) and for the audience you get a wonderful balance between the reflected orchestral sound and the direct vocal sound. If you go to the Royal Opera House (London) or Palais Garnier (Paris) or even a smaller house like Gyndlebourne or the Comischer Oper (Berlin), the absolute best seats to hear a performance from are right at the very top at the very back (often the cheapest seats), but you will hear the most perfect sound. You hear this sort of shimmering effect, the balanced sound, the voice and the orchestra amplified in its own resonating chamber, as though the pit becomes part of the instrument of the orchestra like the body of a violin or the sound board on a piano. It’s an extraordinary experience.

Actually, almost the worst seats are at the first row of the stalls. At the first row, you are very close to the action visually, but the balance between the direct sound coming from the voice and the sound of the orchestra is unmixed and can sound separated. That’s also why when rehearsing for opera, you have somebody sitting in the front few rows balancing from there – normally if the balance is ok right at the front it will work everywhere else.

MF: For some halls, the acoustic conditions might not always be optimal depending on where you sit. The music you hear on stage could also be very different compared to the music you hear in the rest of the hall. How do you prepare for all this?

There are some concert halls where if you sit in the wrong seat, it might be an expensive seat, but if you sit in the wrong seat, it is really not a good experience. In a really good hall, there are very few differences between the seats.

What happens then is, most of the time, conductors or managers never sit in them. They judge performances from a very specific select set of locations. We forget sometimes that if you sit in a different place, you can hear something different.

An orchestra manager some years ago said to me “Look, you need to sit in every seat”. Because you need to know how every one of your audience feels. He was trying to find solutions to make all his audience happy. If we want to inspire people into music we love and make them hear what we want them to hear, we need to make sure we play well for every single seat.

Practically, to do this as a conductor, you often have somebody assisting you whose job is mostly to walk around the hall and give little notes back about how it sounds in the hall. I also find it hugely useful to have assistants, because they can conduct five minutes whilst you can walk around the hall and listen, so that you can really understand the translation from what it sounds like on the podium to what it sounds like in the hall.

There is another trick that I learned from one of my mentors, a conductor called Stanislav Skrowaczewski. 

Stanislav Skrowaczewski - Jonathan Berman
Stanislav Skrowaczewski

He used to occasionally turn 90 degrees to the orchestra, by putting his left ear towards the empty space, to listen to the hall.

You have to work at it a bit, but it gives you a really good sensation of what the hall sounds like, as opposed to when you are facing the orchestra where you hear mostly the direct sounds from the instruments.

Doing this gives you one more bit of information and it allows you can create a better balance between the sound of the orchestra and the reverberation of the hall, hopefully creating a fantastic sounding concert in every seat.

jonathan Berman - orchestra conductor

Interview with Jonathan Berman – Part 1: Presentation and recent activities

 

Marc Fuzellier-Hart: Hi Jonathan, can you introduce yourself and explain how you got into conducting ensembles and orchestras.

Jonathan Berman: Hello, I am Jonathan, an orchestral conductor. I got into music because my family is very musical, so music has always been around me. As a young kid, I learned cello and piano, and I sung which then expanded to organ, harpsichord, viols de gamba, guitar and all sorts of other instruments that I could fit around that.

However, when I was 13-14, I had some wrist injuries from playing piano too much. So I had to give up piano and cello, and actually, all my instruments for about a year. It was during this period that I really wanted to make music and discovered conducting. 

With six other friends, I put on a concert of very small choir pieces. This is when I found that conducting suited me so much better than playing instruments. Even as an instrumentalist I had always wanted to play with other people; I was fascinated not only by sound, but also by its function, its meaning and why composers made certain decisions.

So I found conducting very early on and whilst I was at school, I did little bits of conducting. I was incredibly lucky to essentially go to a specialist music school. There were lots of really good musicians. We had orchestras and choirs that I conducted, then during the summer holidays I would go on conducting courses.

After school, I went to a conservatoire in Holland. I did a Bachelor’s and a Master’s both in conducting, which was an amazing education. I studied with one main teacher for six years, and it was really an old-school apprenticeship more than a college education as I was working as his assistant.

I would often travel with my teacher to his concerts and rehearsals, and it was great seeing the way one conductor would work differently with different orchestras, express things differently, in different countries and in different repertoires.

Now [December 2020] is obviously a very bizarre moment, but in normal times I am lucky enough to travel around the world, conducting orchestras, operas, small groups as well. I do a lot of contemporary music. I really believe that our musical tradition needs to be a living one that connects the past and the present.

 

MF: Yes, it is great to be able to speak to the composer and ask them the way they ideally want the music to be played. And then you can add your own taste and colour.

JB: Absolutely, we spend hours thinking “I wonder what Beethoven meant here”. When you work with living composers like James Macmillan, Mark Turnage or George Benjamin, and you go  “what do you mean by this here?” and you can have an answer. I love that, and I learn so much from the composers I work with. I think it is hugely important to work with people who challenge the boundaries of our creative tradition. 

 

MF: What have been your activities during lockdown?

JB:  Just before lockdown started, I had my first set of cancellations and there was a huge amount of anxiety for all performers. Out of this moment came my first lockdown project – an initiative called ‘ Stand Together Music ’ which I set up with my sister, Imogen, who is very involved in the popular music world. For the first 100 days of lockdown we published a list of every cancelled concert, both classical and non-classical along with daily playlists on Spotify using recordings by cancelled artists.

We ended up curating 12,149 tracks, over 1000 hours of music created by over 10,000 composers/ performers/ orchestras/ bands who all suffered from cancellations. Our aim was to try and encourage people to stream music during (and after) the lockdown consciously so that in some small way we could divert the streaming revenue back to the artists who were suffering cancellations. We also did special features on all UK orchestras, opera houses and many european and international establishments as well.

My other big lockdown project was about making 9 films of and about classical music (which we talk about elsewhere in this blog) – which were nominated and even won some prizes at film festivals – one, unbelievably, for best cinematography!

Jonathan Berman - The Franz Schmidt Project

I was also lucky enough to get into the recording studio just before the first lockdown to start recording a cycle of the complete symphonies of the Austrian composer Franz Schmidt. This is part of a bigger project I have set up – ‘The Franz Schmidt Project’ – to promote his music leading up to his 150th Birthday in 2024.

The backbone of the project will be the complete cycle of his symphonies which I am recording with the BBC National Orchestra of Wales, and through which we will promote Schmidt’s music along with interviews, live performances (throughout the world), radio shows, television broadcasts and talks.

Recording is a fascinating acoustical challenge because microphones don’t pick up sound in the same way ears do – and orchestral sound is a pretty complex sound to begin with!

So in essence, you have three variables on the sound; the playing of the orchestra, the acoustics of the hall and the placing, number, type and balance of microphones.

I am very much a believer in using as few microphones as possible (I think still some of the best sounding recordings ever are the old Mercury Living Presences recordings from the 50’s using three, occasionally only one, Schoeps M201 microphones – even for huge orchestras). Whilst we did have more than three microphones for this recording, the process was the same whereby we tried to get the sound and balance in the room and then replicate that sound through the microphones. We recorded in the beautiful Hoddinott Hall in Cardiff.

 BBC National Orchestra of Wales - Jonathan Berman -  The Franz Schmidt Project

Interestingly my relationship with the BBC National Orchestra of Wales goes back over 10 years and I was at the opening of the hall. It is fascinating to hear how the sound of the hall has changed over the years. It has softened over time. I have noticed the same effect at the Ozawo Hall in Tanglewood (another wooden hall in the USA) whereby each year the sound feels warmer and in particular the upper frequencies soften.

Back to Cardiff, the Hoddinott hall has some wonderful flexible acoustics. On the first day of rehearsals, we found the hall (both on stage and in the recording booth) a little too dry and small for the expansive soundscape of the Schmidt symphony, and so we were able to open some doors, right at the top of the hall to increase the physical volume of the hall until we got a sound that we liked through the microphones.

 

MF: Are you involved in any activities around educating people for music or raising people’s sensitivity to music?

 JB: I don’t have an official position of teaching but I absolutely love to teach conducting. As for raising sensitivity to music, one of our great roles as musicians is to bring people into music and show them what joy there is in actively listening to music.

You know, we have a thousand different types of music and ways to listen depending on the functions in our life. We put music on when we go to the gym, we put music on to sleep, to cover awkward silences in a conversation or just as some kind of background. That is all wonderful. I use music like that. But there is this thing which I love, it can be any genre, you sit, you focus and you engage actively your imagination, your sensitivity; you engage and commit yourself fully in following the music. 

I love bringing people into this way of listening and this world of music.  I love showing them different types of music, different pieces of the same composer that they know or letting them see some aspects of a certain piece of music. It really gets me going and I want to share that with people. Musical understanding is not something that you either have or don’t have – a clandestine group of those in the know. There are many pieces, composers which at first hearing I didn’t understand or didn’t even like. But through time, through multiple listenings, through listening to others talk about this music, I have come to absolutely adore these pieces and composers.

I recently filmed a series called Postcards from Vienna, where I talk about viennese music. Along with an amazing woman called Emily Ingram (co-founder and CEO at Onjam), we made four episodes of this documentary about classical music along with five other classical music movies. They are not just video performances, but videos that somehow visually draw people into the underlying structures, images, ideas, associations, illusions within a piece of music. All of these movies were trying to create, in different ways, environments for people to get closer to this active way of listening and interacting with music.

Jonathan Berman - Postcards from Vienna

The first we did, during lockdown, was the Goldberg Variations with a Dutch string trio. They were combined with Sir Simon Russell Beale reading texts, all about solitude and photographs from the artist Kristina Feldhammer.

Then we did a video of Stravinsky Septet where we created new artworks inspired by artists who connected with the period of Stravinsky’s work. Natalia Goncherova, Sonya Delauney and Lyubov Popov for the first ‘Ballet Russe’ movement, Mark Rothko for the middle movement and then we recreated the process of painting Lee Kransner Abstract Expressionist painting.

I wanted to show and to visualise that for Stravinsky in the Septet. He is developing and discovering formal processes and putting them either onto something old fashioned or something really new. However, he is not writing a piece of music about the formal processes, but in fact the opposite. He is using the formal process to create character, emotion and direction – just music!

My idea is that, without actually educating people, without being a teacher and say “this is what happens, you go and learn it”, you can provide them a key into something that is not simplistic but nuanced and complex. You don’t have to talk or express it with complexity.

I tried in the movies to realise these ideas using the visual elements of films. Pictures say a thousand words. In the documentary series of Postcards from Vienna (where I talk about music), I don’t use musical terms or long words. I try to visualise the musical processes and the decisions of the composers.

8 reasons why you should engage acoustic designers very early on mass timber projects

 

Mass timber constructions pose particular challenges for acoustic engineers. 

This is why the acoustic design for mass timber buildings needs to be considered earlier than on more traditional buildings. Doing this can have positive consequences on the budget, the comfort of the occupiers and the sustainability of the building. 

This post gives you 8 reasons why you should follow this advice.

 

  01

To take account of the weaknesses at low-frequencies  

Timber constructions are known for their sound insulation weaknesses at low frequencies. This usually leads to a reduction of comfort for the occupiers.

A common problem in timber constructions is the disturbing audibility of people walking on floors.  

Depending on the country, the local building regulations might not consider the right frequency range. Baring this in mind, the acoustic designer is likely to recommend the extension of the design brief for some parts of the building. For more details on this topic, check Why we need to think beyond building regs for the sound insulation of CLT constructions .

Be aware of the consequences though! Setting these types of extensions can lead to needing more materials, implementing specific design methods and probably needing more space.

Therefore, you need to consider this as early as possible in the planning to avoid any unexpected loss of space or increase of the construction cost.

Although, there is always room for optimisation, which the acoustic designer will help you with. 

02

To know how much mass is needed from the start

 

Along with cavities and decoupling methods, the acoustic designer relies on adding mass to improve the sound insulation performance of the partitions. 

Timber structures being very light, you really can’t avoid needing to add mass to most separations. At least, those that are acoustically rated. 

Adding mass could result in a structure significantly heavier than originally planned.

Not taking onboard the need for a minimum of mass early enough in the design, could lead to surprises during the later design stages. To the point of having to re-design the structure and maybe the foundations to take account of the extra load. 

03

To decide early on the reliance of dry and wet solutions 

If not for sustainability and speed of construction, acoustic consultants would advise implementing wet solutions in timber buildings (i.e. using concrete and plaster generally).

The advantages are:

  • they are made with dense materials that are very useful in adding  mass to the constructions.
  • because the materials are dense, you can minimise the thickness of the layers and lose less space in the buildings.
  • they can increase the internal vibration damping and the stiffness of the separations.
  • to a certain extent, they can fill the gaps between the timber elements.

However, dry solutions are preferred for timber buildings because the materials involved are generally less harmful to the environment, quicker to install and lighter. Three strengths mass timber constructions are very well known for.

The design techniques, materials and products to control the sound insulation with wet and dry solutions can be very different. To the point that changing from wet to dry (and vice-versa) in the middle of a design can lead to re-budgeting and sometimes re-designing

So it is best to decide as early as possible, with the acoustic consultant, whether the design will rely on wet and/or dry construction methods.

04

To optimise the building layout and stay on budget 

Let’s face it: controlling the transmission of sound between spaces in timber buildings is challenging!

To comply with the design brief, the acoustic consultant will advise for more mass, more materials and more products. All of these are likely to increase construction cost.

To minimise this and stay on budget, you can work with the acoustic consultant by optimising the building layout to separate and disconnect the loud and sensitive spaces as much as possible. 

This way, you will reduce the reliance of expensive measures to control the sound transmission between the spaces. 

Working on the building layout can also help you minimise the embodied carbon of the building. See Reason 7.

 

Note: The above is not just applicable to timber buildings but to any type of building.

05

To plan for the right amount of space

As discussed above, sound insulation design is based on associating mass, decoupling methods and cavities. 

But because timber is a light material, the acoustic consultant compensates on the two latter leading separations to be generally thicker and wider.

Also, the materials used in dry solutions are not always as dense as those in used in wet solutions. So if you design your building with dry solutions and need a minimum amount of mass, it is likely that the heavy layers will need to be rather thick compared to those of wet solutions.

By knowing all the above, you can plan early for enough space between the rooms and avoid having to compromise on room size later down the line.  

06

The acoustic and structural engineers need to work together early

For mass timber projects, the acoustic design should ideally be considered at the same time as the structural design. 

This is not just because more mass creates a higher load as discussed in Reason 2. It is also to work on suitable design methods to control the vibrations transmitted to/between the building elements.

 

Note: Vibrating elements can re-radiate audible sound. But it depends on a few different factors. 

 

The acoustic and the structural engineers could work together on:

 

  • the connections between the elements: depending on the fixing method, more or less vibrations are transmitted between the timber elements. The same goes with the way the elements are in contact with each other. 
  • cavity breaks: they can be efficient at controlling vibrations, but might not always be possible to have for structural and cost reasons.
  • stiffening some separations: different methods exist to do this. You could either add more mass, connect stiffer elements with a certain degree of bonding or also reduce the spans/spacing between the structural elements.

Why is stiffening the separations important? Because it is one way to increase their sound insulation performance at low frequencies. 

07

To minimise the embodied carbon and increase the sustainability of the building 

Acoustic design is not very environmentally friendly.

It often relies on materials that are not sustainable or require a certain amount of energy (emitting CO2) to be produced. 

In other words, acoustic design has the potential to screw up your plans for net-zero carbon!

If you start working early with the acoustic consultant, he/she can help you minimise this by working on:

 

  • the building layout. As discussed in Reason 4, optimising the building layout is likely to reduce the use of mass, materials and products to comply with the design brief. This process can therefore have a positive impact on the embodied carbon of the building.
  • implementing sustainable design methods. The main thing here is to go for dry solutions as much as possible. They use more materials and products that are sustainable and require less energy to be produced. As discussed, in Reason 3, implementing dry solutions is a choice to make as early as possible. 
  • using sustainable products.  This choice doesn’t necessarily need to be made early in the design. Although, you might need to consider some products early as extra tests could be required. See the following paragraph for more details.

08

To plan for further possible testing

Depending on the situation, the acoustic consultant might recommend testing specific solutions because:

 

  • They have never been tested.
  • They have been tested but some performance data or details are missing.
  • They have been tested, but not under the right conditions.

 

This is more likely to happen for timber buildings, especially when the solutions are related to sound insulation design.

It is known that, in controlling the sound insulation within timber buildings, some materials have a different efficiency on timber structures than on masonry structures.

In other words, if a material has a certain performance on a masonry construction, it doesn’t mean it will achieve the same performance on a timber construction. So you could need to re-test the material on a timber construction. (resilient layers, that help control the impact sound insulation of floor constructions, are probably the best example).

Also, a material/product might have already been tested, but the data or the testing methods are limited.

It is usually the case for the frequency range considered that doesn’t go below 100 Hz, when acoustic designers need data down to at least 50 Hz (if not 20 Hz).

For impact sound insulation testing, it is good to use a calibrated impact ball (as well as the traditional tapping machine) which is not often used to test masonry floor constructions. 

Finally, we know that the sound insulation performance of mass timber elements can dramatically vary with the mounting conditions (i.e. fixings, spans and also spacing between structural elements). If the proposed mounting conditions hugely differ from those already tested, it might be necessary to undertake more tests (in a lab or on-site).

 

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Sound reverberation – Part 2: Specialist indices 

 

If you design a new performance space, you want to know how the musical or speech-based activities will be heard.

Or similarly, you might want to establish the acoustic conditions of an existing performance space.

As part of the assessment, you generally need to ask yourself: 

  • is the space going to be too dead or too live for the type of performances planned?
  • are the performances going to be clear and/or intelligible to the audience?
  • are performances going to sound too quiet or too loud … or just right?
  • is the space (especially during musical performances) going to sound too dry or too boomy? 

Part 2 here goes through some specialist acoustic indices that help to objectively answer the above questions.

These indices are:

  • the Early Decay Time (EDT).
  • the Sound Strength (G).
  • the Objective Clarity (C80) or Definition (D50).
  • the Early Lateral Fraction Energy (LF).

Rather than showing very technical data and complicated formulas, it intends to shed some light on which parts of the sound reverberation are used to assess the acoustic qualities of a space.

To better understand this section, you could read Sound reverberation – Part 1: Basics first. It explains what the sound reverberation is, how it is measured and what the reverberation time index is.

 

Note: this post is based on the following documents:

  • Auditorium Acoustics and Architectural Design – Mike Barron;

  • Concert halls and Opera Houses – Music, Acoustics and Architecture – Leo Beranek

  • ISO 3382-1: 2009 – Acoustics — Measurement of room acoustic parameters — Part 1: Performance spaces

 

 

Early decay time (EDT)

 

 

As its name says, the EDT is a measure of how fast (or not) the early sound energy decreases in a room. The quicker the early reverberation dies, the shorter the EDT.

Technically, it is based on measuring how long the early energy takes to decay by 10 dB (excluding the direct sound from the source).

The EDT is very often used for the (re)design of music performance venues and relates to the perception of acoustic reverberance.

 

 

 

 

 

 

 

 

 

 

 

Early decay time - 10 dB - sound reverberation - sound energy decay
Calculation of Early Decay Time

 

 

 

 

 

In the table below, you can see some examples of preferred EDT values (in seconds) for different types of musical performances.

Types of spacesPreferable Early Decay Time (EDT) values
Symphonic repertoire
(over 1400 seats)
2.2 s EDT500-1000Hz* 2.6 s
Chamber music
(under 700 seats)
1.9 s EDT500-1000Hz* 2.3 s
Opera
(over 1200 seats)
1.5 s EDT500-1000Hz* 1.9 s
*EDT500-1000Hz : average of Early Decay Time at 500 Hz and 1000 Hz (in unoccupied conditions)

 

Examples of preferable Early Decay Time values

You can see that the EDT values are shorter for opera performances than for chamber music and symphonic music performances.

This means that you want the early reverberation to die quicker for opera music than for chamber music and symphonic music.

 

Sound Strength (G)

 

 

The Sound Strength (G) relates to how loud (or quiet) sound sources might be perceived in a room. In a way, it characterises the amplification power of the room. 

You can measure G using an omnidirectional sound source and compare:

  • the acoustic energy of that source at a given point, against;

 

  • the energy of the same source, located 10m away from the receiving position, in an environment with no sound reflecting surfaces (conditions found in anechoic chambers).

 

 

 

 

 

 

Sound Strength - G - omnidirectional source - sound reverberation - free field - sound energy
Calculation of Sound Strength (G)

The sound strength is measured in dB and usually ranges between 0 and +10 dB in performance venues.

In the table below, you can see some examples of preferred values for different types of musical performances.

Types of spacesPreferable Sound Strength (G) values
Symphonic repertoire
(over 1400 seats)
1.5 dB Gmid* 5.5 dB
Chamber music
(under 700 seats)
9 dB Gmid* 13 dB
Opera
(over 1200 seats)
-1 dB Gmid* 2 dB
*Gmid : average of Sound Strength at 500 Hz and 1000 Hz

 

 

Examples of preferable Sound Strengths values

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What do these values tell us?

 

The preferred values are mostly positive. This means spaces need to amplify the sound of performances. Which makes sense, especially for the more remote seats where you also want to hear the quieter instruments and sound details of the performances.

The preferred ranges have different upper limits. This shows that each type of performance has its own preferred level of amplification above which music might sound too loud and unpleasant.

The preferred values for chamber music are higher than for symphonic repertoire and for opera. This means that spaces for chamber music performances require a higher sound amplification. This makes sense because the instruments and ensembles involved in chamber music are respectively quieter and smaller than those involved in symphonic repertoire or opera.

The values presented are averages over 500 and 1000 Hz frequency bands (i.e. mid frequencies). At low frequencies (especially around 125 Hz), for symphonic music, the sound strength is preferred to range slightly higher between 3.0 and 6.0 dB. This corresponds to a preference for rather warm reverberation conditions that amplify the base sounds more than the medium sounds.

Objective Clarity (C80) and Definition (D50)

Whilst the objective Clarity (C80) helps to assess the clarity of musical performances in a space, the Definition (D50, also called Deutlichkeit) is for the intelligibility of speech-based performances.

 

 

 

Note: Musical clarity corresponds to the ability to hear the musical details

 

Both metrics are based on comparing early sound energy against the late or total sound energy arriving at a listening position. 

For the C80, you compare the energy arriving within the first 80 ms against the rest of the energy.

For the D50, you compare the energy arriving within the first 50 ms against the total of the energy.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: The average duration of speech sounds is around approximately 70 ms.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Objective Clarity - C80 - sound reverberation - free field - sound energy
Calculation of the Clarity (C80)

 

 

 

 

Calculation of Definition (D50)

The Definition has no unit and the preferred values range between 0.3 and 0.7. 

The Clarity is measured in dB. In the table below, you can see some examples of preferred values for different types of musical performances. 

Types of spacesPreferable Clarity (C80) values
Symphonic repertoire
(over 1400 seats)
-3 dB C80,3* 0 dB
Chamber music
(under 700 seats)
-2 dB C80,3* 2 dB
Opera
(over 1200 seats)
1 dB C80,3* 3 dB
*C80,3 : average of Clarity at 500 Hz, 1000 Hz and 2000 Hz

Examples of preferable Clarity values

 

 

 

 

 

 

 

 

 

 

 

 

 

What do these values tell us?

  • The ranges imply that a balance is desired between the early energy and the total or rest of the energy.
  • The more the early energy, the higher the values, the clearer the speech/musical messages.
  • The C80 values for Opera performances are higher than the preferred values for chamber music and symphonic music. This translates the need for more reflected sound arriving early to the listeners. This makes sense as enjoying opera performances depends on clearly understanding the musical and sung messages.
  • In comparison, the preferred values are lower for symphonic music, meaning that hearing every single musical detail is not as important and blending of musical sounds is more preferable.

Early Lateral Fraction energy (LF)

The Early Lateral Fraction energy (LF), also called the objective source broadening, considers some spatial aspects of the sound reverberation.

 

 

The metric is an objective measure of two spatial impressions:

  • a sound source becoming broader to a listener as it becomes louder.
  • the sound surrounding a listener, giving a sense of envelopment.

 

 

For musical performances, the perceived broadening of a sound source and the envelopment are both desired to create a sense of spaciousness. This is largely influenced by early reflections arriving in lateral directions to a listener. 

Hence why you calculate LF by comparing, within the first 80 ms, the sound energy arriving to the sides against the sound energy arriving in all directions.

Calculation of Early lateral fraction energy
Calculation of Early Lateral Fraction energy

 

 

 

 

 

 

 

 

 

 

 

The early lateral fraction energy has no unit. It is averaged from 125 Hz and 1000 Hz and it is generally preferred to range between 0.05 and 0.35. 

 

Other acoustic indices

Other important indices not mentioned above are:

 

 

 

 

  • Speech Transmission Index (STI): It measures the intelligibility of speech-based messages and is very often used to design Public Address Voice Alarm (PAVA) systems. Calculating the STI in a space at a specific location is complex. It depends on the speech level, the frequency content of the message, the background noise level in the space, the quality of the audio equipment and also the sound reverberation in the room;
  • Early Support (STearly) and Late Support (STlate): They are two measures of the acoustic conditions for music ensembles and concentrates on the very early sound reverberation. Stage acoustic science (based on the acoustic conditions musicians prefer to play in) has recently seen extensive progress thanks to the development of new audio reproduction techniques and computer modelling. Focus has been on the spatial and spectral (i.e. frequency related) aspects of the reverberation on stages.  

Conclusion on acoustic design

As discussed above, one key design aspect for performance venues is to study the way sound is reverberated inside.

For different listening positions, the acoustic designer works on:

 

 

 

 

 

  • controlling how fast the reverberated sound energy decreases within the space.
  • managing the natural sound amplification of the space depending on the music played.
  • controlling the frequency content of the reverberated sound.
  • finding the right balance between the early and late sound energies arriving at the listening positions.
  • controlling the directions in which the (early) sound energy arrives at the listening positions.

All the above mainly depend on the location and shape of the surfaces within the space, the volume of the space and the acoustic properties of the finishes. 

 

 

 

 

Sound reverberation – Part 1: Basics

 

Do you work on building projects and would like to know more about sound reverberation so that you can better understand part of the acoustic design? Then this series of posts is for you. 

Part 1 (here) takes you through the very basics of sound reverberation including:

  • What sound reverberation is.
  • How sound reverberation is measured.
  • What the reverberation time is.

Part 2 will shed light on some specialist indices used for the design of spaces for spoken and/or musical performances. 

And finally, Part 3 will explain some of the basic principles of reverberation control.

 

What is sound reverberation?

Reverberation happens in a space when the sound of a source is reflected into multiple reflections. They build up and decay as they are absorbed by the surfaces and the furnishing.

The reverberation characteristics of a room make its acoustic footprint. A little bit like an instrument responding to an excitation with its own timbre. 

Acousticians study sound reverberation because it directly influences:

  • the intelligibility of speech 
  • the clarity and warmth of music
  • (when it is particularly high) the background noise
sound reflections - sound reverberation
Sound reflections

Sound reflections are often represented as rays traveling in different directions and arriving at different times. Each ray transports acoustic energy and loses some amount as it travels through the air or hits an obstacle.

The sound reverberation in a space depends on a few different aspects including:

  • the acoustic properties of the surfaces and finishes 
  • the location of the surfaces 
  • the location of the source and the receiver 
  • the volume of the space 

The ideal reverberation conditions for a room depend on its use. Some spaces (like classrooms or recording studios) need rather “dead”  reverberation characteristics. Others need a medium reverberation (like assembly halls, theatres for drama, concert spaces for amplified music, etc), whilst others work best when they are very reverberant (large symphony halls for acoustic music, spaces for choral music, etc).

 

How do we measure sound reverberation?

You can generally study sound reverberation by analysing how the sound energy evolves in a room after a short sound burst or after a source is interrupted (there are other measurement methods but they won’t be discussed here). Its basically observing how a room behaves under a sound excitation. 

You can analyse the reverberated sound energy in different ways:

  • in sound pressure level. 
  • in duration: how long it takes for some or all the sound to partially or entirely disappear.
  • in arrival time: when does the reflected sound arrive to a receiving location. You can split the reverberation into three different parts:
    • the direct sound
    • the early reflections
    • the late reflections

From the representation of sound as rays, you can come up with the diagram to the right commonly called a reflectogram

Sound reverberation: Direct sound, early reflections and late reflections
Sound reverberation: Direct sound, early reflections and late reflections
  • in frequency: what is the frequency content of the reflected sound. To do this, the sound energy is filtered for different frequency bands that generally range from 63 Hz to 8000 Hz.
Frequency band filtering of impulse response - 63 Hz - 125 Hz - 250 Hz - 500 Hz - 1000 Hz - 2000 Hz - 4000 Hz - 8000 Hz
Frequency band filtering 

Note: Most buildings are acoustically designed for people to be able to hear, communicate, concentrate or even rest comfortably. So because the human ear is more sensitive at mid-frequencies and the human voice emits sound around the mid-frequencies, the acoustic designer generally concentrates on the reverberation conditions at 500 Hz, 1000 Hz and 2000 Hz. 

Sometimes, it is also important to control the reverberation conditions at low frequencies. This is discussed a little bit more below.  

 

  • in space: where the reflected sound arrives from to a listener, i.e. to the top, to the back, to the bottom or to the sides of the listener’s head.
    Spatial sound reflections

Depending on the use of a space and the acoustic characteristics you want to concentrate on, you can either isolate or combine the above aspects.

For example, you can:

  • measure how fast the reverberated sound disappears; you will have an idea of how echoey a room might be.
  • compare the sound energy arriving within the first 50ms against the total energy; you will have an indication of how intelligible a spoken message could be. 
  • compare (during the first 80ms) the energy arriving to the sides of a listener against the energy arriving in any direction; you will have an indication of how surrounded by sound a listener might feel and how broad a source might be perceived (this is particularly useful to know for spaces where acoustic music is played).
  • compare the energy of a source with the rest of the reverberated sound against the energy of just the source; you will have an idea on amplification power of a room. 

 

Note: the above examples come from very standardised processes, and for ease of understanding, they have been simplified. More details are given in Part 2 of the series. 

 

All the above aspects are quantified with particular acoustic indices that are psychoacoustic based. 

The section below concentrates on the reverberation time index, which is the starting point of any sound reverberation design.

Part 2 (published soon) will present some specialist indices that are very useful for the design of spaces for spoken or musical performances. 

 

Note: you can find more details in the following documents that were reviewed to write these posts:

  • Auditorium Acoustics and Architectural Design – Mike Barron;

  • Concert halls and Opera Houses – Music, Acoustics and Architecture – Leo Beranek

  • ISO 3382-1: 2009 – Acoustics — Measurement of room acoustic parameters — Part 1: Performance spaces

  • BB93: acoustic design of schools – performance standards .

 

Reverberation time (RT or T)

 

The reverberation time (RT) is the one index that acousticians use to rate or design reverberation characteristics. Practically, it tells you how long it takes for sound to disappear in a room.

Reverberant spaces, like churches, have higher reverberation times than acoustically “dead” spaces, like recording studios.

In more technical terms, you analyse the impulse response and measure how long (in seconds) it takes for the acoustic energy to decay by 60 dB.

energy decay - reverberation time calculation - 60 dB
Sound energy decay and reverberation time calculation

As explained above, the impulse response is filtered for different frequency bands (between 63 Hz to 8000 Hz) and the RT is measured from each energy decay. The RT is measured in different frequencies generally ranging from 63 Hz to 8000 Hz. 

Energy decay calculation for each frequency octave band - 63 Hz - 125 Hz - 250 Hz - 500 Hz - 1000 Hz - 2000 Hz - 4000 Hz - 8000 Hz - reverberation time - frequency band filtering
Energy decay calculation for each frequency octave band

follow on note from above: as mentioned above, the acoustic designer generally concentrates on the reverberation conditions at 500 Hz, 1000 Hz and 2000 Hz, the mid frequencies. Therefore, the RT targets are generally an average of some or all the values of 500 Hz, 1000 Hz and 2000 Hz frequency bands.

Hence Tmf  (used for example in education spaces) which is the average of the reverberation time values at mid frequencies.

 

Sometines, it will be important to consider the reverberation time at frequencies lower than 500 Hz.

This is the case for medium to large spaces where acoustic music is played. Compared to the mid and high frequencies (500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz), a controlled increase of the reverberation time at low frequencies (63 Hz, 125 Hz and 250 Hz) create warmer listening conditions.

For Special Education Needs (SEN) classrooms, specific design requirements are in place in a wide range of frequencies, including at the frequency bands 125 Hz and 250 Hz. This is because too much low frequency reverberation can mask the sound of the teacher’s voice and make it harder to clearly hear what (s)he says (see Acoustic Design of SEN (Special Educationnal Needs) classrooms  for more information on the acoustic design of such rooms).

The table below shows some examples of preferable reverberation times for different spaces and music repertoire.

Note the different frequencies you need to consider depending on the situation.  

 

Types of spacesPreferable reverberation times
Tmf1T500-1000Hz2T125-4000Hz3T4
SEN Classrooms 0.4 s 0.4 s
Recording Studios 0.5 s
Secondary Classrooms 0.8 s
Offices 1.0 s
Sports halls 1.5 - 2.0 s

(volume dependent)
Symphonic repertoire
(over 1400 seats)
1.8 s T500-1000Hz 2.1 s
Chamber music
(under 700 seats)
1.6 s T500-1000Hz 1.8 s
Opera
(over 1200 seats)
1.4 s T500-1000Hz 1.6 s
1Tmf : average of reverberation times at 500 Hz, 1000 Hz and 2000 Hz (in unoccupied conditions)
2T500-1000Hz : average of reverberation times at 500 Hz and 1000 Hz (in occupied conditions)
3T125-4000Hz : average of reverberation times from 125 Hz to 4000 Hz (in unoccupied conditions)
4T : reverberation time in any frequency band between 125 Hz and 4000 Hz (in unoccupied conditions)

Examples of preferable reverberation times

 

 

 

 

Acoustic design for SEN (Special Educational Needs) classrooms - absorptive suspended ceiling - acoustic wall panels - acoustic carpet

Acoustic design of SEN (Special Educational Needs) classrooms

If you design a school, you will probably need to have at least one SEN (Special Educational Needs) classroom.

Given the very specific acoustic design requirements of such spaces, this post sheds light on:

  • why the acoustic environment is important for SEN classrooms.
  • what type of acoustic environment is suitable for SEN classrooms.
  • what you need to think about for the acoustic design of SEN classrooms.

This post mostly draws on the following British documentation:

 

Why is the acoustic environment important for SEN classrooms?

Some pupils in SEN classrooms will have special hearing requirements

As listed in the Acoustic of Schools: a design guide, these pupils could be those:

 

  • with visual or permanent hearing impairment
  • with fluctuating hearing impairments caused by conductive hearing loss
  • with speech, language and communication difficulties         

 

  • whose first language is not English
  • with autistic spectrum disorder (ASD)
  • with an auditory processing disorder or difficulty
  • with attention deficit hyperactivity disorders (ADHD)

 

Of course, the ability of the teachers to organise and manage the SEN classrooms is paramount. But the acoustic environment also has to be suitable for these pupils to be able to hear, concentrate, learn and communicate. 

 

What type of acoustic environment is suitable SEN Classrooms?

If you design a (several) room(s) for pupils with special hearing requirements, you need to be aware that the acoustic quality of the environments will have to be a step further compared to most standard school spaces. 

Generally, you will need:

  • Quieter environments.
  • Less reverberant (or less echoey) environments, especially at low frequencies. Too much low frequency reverberation can mask the sound of the teacher’s voice and make it harder to clearly hear what (s)he says (If you need to better understand what sound reverberation is, you can read Sound reverberation – Part 1: Basics).

 

Note: For open-plan spaces, BB93 states the following:

Open plan teaching and learning spaces should not be regarded as a simple alternative to traditional classrooms and may be unsuitable for some children, particularly those with special hearing or communication needs.

In order to fulfill their duties under the Equality Act 37 2010, school client bodies should anticipate the needs of deaf and other disabled children as current and potential future users of the space when open plan accommodation is being considered.”

 

What do you need to think about for the acoustic design of SEN Classrooms?

Quiet environments

To design quieter environments, you could need to control the noise from various areas. 

First, you need to control the noise from outside. This could include:

  • Designing the building façade to control the external noise breaking into the classroom.
  • Selecting the right ventilation strategy. The external noise environment could be too loud to ventilate the rooms by simply opening the windows. Even during the hottest days of the year. In this case, you need to set a suitable mechanical ventilation strategy.

    Note: under BB93, the internal noise level requirements in schools can be relaxed to improve thermal comfort in summer (during the hottest 200 hours in peak summertime exactly) at the expense of high indoor ambient noise levels. But this relaxation doesn’t apply to SEN classrooms!

 

mechanical ventilation strategy - sealed windows - not opening windows - Variable air volume system - building services noise control - SEN (Special Educational Needs) classrooms
Mechanical ventilation strategy for SEN classrooms

 

Secondly, you need to control the noise from the services installed for the school, like the ventilation systems and/or heating & cooling systems. They are likely to require:

  • Attenuators to control the fan noise transmitted through the ductwork.
  • If some units (for example fan coil units, heat recovery units, VAV boxes, etc) are hung from the soffit, you could need a dense and sealed suspended ceiling to control the noise from the units themselves. Alternatively, sealed cupboards or encasement systems made with dense materials could be required if the units are in other places of the room.

 

mechanical ventilation strategy - dense suspended ceiling for sound insulation - eat recovery units - Variable air volume system - building services noise control - SEN (Special Educational Needs) classrooms
Noise control of services (examples)

 

  • Controlling the noise from inside the school by improving the sound insulation of the floors, walls and doors that separate the SEN spaces from other spaces. Zoning the SEN rooms and/or creating buffer spaces around them is also possible.

Less reverberant environments

To create environments that are less reverberant, especially at low frequencies, an efficient acoustic design could involve the following:

  • Installing more acoustic absorption on the walls or fixed on/hung from the soffit.
  • Installing some materials or elements that absorb more acoustic energy at low frequencies. You can efficiently do this by installing a dense porous suspended ceiling with a (large) cavity above.
  • Planning smaller spaces, as the smaller the volume the less reverberant (echoey). SEN rooms are generally smaller anyway, hosting between 4 to 8 pupils most of the time.
  • Laying a carpet. On its own, a carpet will not make you achieve the reverberation time you target for a classroom. However, it can help you reduce the need for (expensive) acoustic materials.

 

Reverberation control design for an SEN room - acoustic suspended ceiling - acoustic wall panels - Carpet
Example of sound absorption design for SEN classrooms

 

Design Note: Sometimes it might not be practically possible to achieve the very stringent sound reverberation requirements for SEN classrooms. 

In this case, you can raise an Alternative Performance Standard (APS). You will need to justify why you can’t practically (and not financially!) achieve the initial requirement and suggest an alternative performance with the help of the acoustic consultant. BB93 documents a thorough procedure to follow for Alternative Performance Standards.

 

Procurement tip: During the early stages of a school project, it is normal to have minimum specifications for the acoustic absorption materials proposed in each space. They will generally be selected in terms of acoustic absorption Classes (i.e. A, B, C, D, …).

As the detailed design approaches, you will have a better idea of the products you want to use. 

Once the products are selected, it might be useful to ask the acoustic consultant to review the quantities of materials. This will involve gathering the absorption test data for the specific products and re-running the calculations. By doing this, you are likely to reduce the quantities of materials and therefore reduce cost.

 

 

 

 

Sir James MacMillan in the Sistine Chapel

 

Interview of Sir James MacMillan – Part 2: Memorable venues

 

In the first part  of this interview, James was telling us about his origins, where his passion for music comes from, and the music festival for which he is the founder and artistic director,The Cumnock Tryst. He also talks about his involvement in music education, his vision for teaching music composition and his opinion on why acoustic design is so important for music schools. 

In the second part below, James shares his experience of visiting the Sistine Chapel, in Rome, where The Sixteen orchestra and a string orchestra played his music. He also shares his experience of attending some famous venues either as a performer or as part of the audience.

 

 

MF: What are your experiences and opinions on the acoustics of music venues?

JMM: It is something that musicians talk about all the time. We are obsessed about acoustics, we are obsessed about how music sounds in every hall that we go to. Musicians are always comparing acoustical experiences of one hall against another, what kind of music works best in this place, what kind of music works best there.

There has been a revolution in thinking how we approach pre-baroque music both in instrumental music and choral music. That has involved a historical way of thinking and researching what the instruments were like, what the venues would have been like and how various music would have been performed.

A few years ago, The Sixteen (conducted by Harry Christophers) and a string orchestra (the Britten Sinfonia to begin with) were invited to the Sistine Chapel in Rome to perform a piece that I wrote. Now, not many modern performers go to the Sistine Chapel and know what the acoustics of the Sistine Chapel are like. It is not heard much, it is not a big place, but it is where the likes of Palestrina would have directed his choruses. Palestrina and Lasses, who just came to pray, made their great masses just for that space. Yes, the music is shaped by that liturgical, theological and religious aspiration, but the acoustic of the chapel is just as important. The music has to unfold at a certain pace. It can’t be too fast, otherwise it would get lost. It had to be heard properly as it was made at a time where ecclesiasticals were getting worried about people not hearing the words properly.

When we turned up a few years ago to perform the Stabat Mater, no one had any idea of what the hall would sound like. However, as soon as they started playing and singing, I saw the delight and the relief on the musicians faces when they realised what a wonderful space it was. That was an incredible acoustical experiment for all of us.

I also entered the choir gallery where Josquin des Prez had been and Palestrina had sung. Even Allegri who wrote the great Allegri Miserere had been heard by Mozart in that very space. All those musicians had been there before, and there was one wonderful moment when I returned to the little choir garden. I saw Josquin des Prez’s signature scribbled onto the wall. He had written “Josquin was here”. An amazing moment for a composer who loves that tradition and history.

There are some spaces that work incredibly well for certain types of music and singers, whilst others suit instrumental music better.

Orchestral music works better in places like the Concertgebouw in Amsterdam or the Musikverein in Vienna. They are regarded as almost near perfection for music of the classical world, especially for music of the 18th and 19th centuries. I certainly hold up these places as the perfect example.

The more modern halls in the UK that work for me are the Bridgewater Hall in Manchester and of course the Symphony Hall in Birmingham. They are the two best halls musicians talk about in the whole of the UK. Musicians much prefer to play there than at the Barbican, in London, or the Royal Festival Hall at the Southbank Centre that are regarded as problematic acoustically (for more information,  read What is Wrong with London’s Concert Halls https://acousticengineering.wordpress.com/2015/03/09/what-is-wrong-with-londons-concert-halls/ written by Trevor Cox). Up here in Scotland, another problematic hall is the Glasgow Royal Concert Hall which lacks the warmth and the depth that the Symphony Hall and the Bridgewater Hall have.

MF: What are your most memorable venues, not just for acoustics, but also for the internal comfort?

Sir James MacMillan
© Marc Marnie 2019

JMM: I must single out the Concertgebouw as a very special place. Every musician I know loves performing there. I have conducted there a few times. I have conducted my own music, I have conducted other composer’s music, older music, choirs and orchestras in there. I have also heard choirs and orchestras, sometimes separately sometimes together. It is a very special place, and not just for what you can make of the acoustic. A musician can feel at home in a place like that, the accommodation is very spacious backstage. You can prepare well and there is a wonderful sense that you can relax into the space for rehearsals and prepare psychologically. You are made to feel at home. The initial and sole purpose of the place is for making music excellently.

The conductors have very good spaces. I love the fact that when I go there, I have a very private and comfortable space where I hear nothing. I don’t hear the musicians rehearsing, I am away from the audience and I can be in solitude, which exists until the very moment I go onto the stage. Having that sense of isolation before you go on stage is vital because you live in the music. It is just you and the music, anything else is a distraction. Every conductor has their own way to prepare psychologically for stepping onto the stage. Some do yoga, some contemplate, some pray. It requires a kind of emptying out. You engage with silence, because in that silence you encounter the music, and when you go on stage with only the music in your head, you can perform better. The way a musician prepares is so vital, whether it is a conductor or even an orchestra member. You have to be in a good frame of mind in order to perform at your best. So maybe that is another design aspect to take on board: giving the opportunity to prepare well.

MF:  The Concertgebouw is shoebox-shaped. Another very popular hall shape for concert halls is the “vineyard” shape. Have you got any experience in conducting in these sorts of halls?

JMM:  I have less experience in that kind of hall and I hear different accounts of which halls are good or not. I have heard very different accounts at the Elbphilarmonie, in Hamburg. Some who love it, some who don’t. I don’t know what to make of that. I suppose there might be a little bit more nervousness amongst musicians about that particular shape. I don’t know why but I certainly have less experience of the vineyard shape.

MF: Finally, times are pretty tough for the performing arts world at the moment. How have COVID and lockdown affected you and your activity? (reminder that the interview was done a few weeks ago)

JMM: In some ways, some things haven’t changed. I am a composer and I need silence and solitude to go on with writing music. In a sense, lockdown is life as normal for me and that is the case for most composers. But we don’t live in a bubble, we don’t live in splendid isolation and we know that writing music is a statement of hope for the future.

It is a statement of hope that will go into the hands of interpreters who will then express that music and communicate its message and its meaning to an audience. One writes in a splendid isolation but it is writing for the future. One is writing for ones furloughed or redundant human beings otherwise it is pointless.

Although we live and work in silence, it is not an island of no communication. It has a breathing ground of thought and creativity that eventually is able to get the music out there. So, in that sense, life goes on as usual. 

However, all my performances have come to an end. For every performing musician, nothing is happening. Certainly not in this country. Things are beginning to open up in other countries. I noticed that there are performances in Austria. Some people have been in touch from Denmark and France recently. Even in Wuhan, life has got back to normal with big concerts. These are messages of hope. If it is happening elsewhere, with caution in mind of course, one hopes that life will come back here. I suppose the green shoots are also happening in places like Wigmore Hall which has come back to normal with chamber music concerts performed to smaller audiences.

I met my first orchestra for the first time a few weeks ago. We recorded the video and the audio of new music from young composers that the orchestra will put on its website. I have a recording session with an orchestra for BBC Radio 3 in a few weeks in London. These are incredibly exciting moments and hopefully there will be more in the months to come.

 

 

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Sir James MacMillan Conducting

 

Interview with Sir James MacMillan – Part 1: Origins and The Cumnock Tryst

 

Back in October, Sir James MacMillan very kindly accepted to answer my questions and I can’t thank him enough for this.

This interview has been split into two parts.

In the first part (here), James tells us about his origins, where his passion for music comes from, and the music festival for which he is the founder and artistic director, The Cumnock Tryst. He also talks about his involvement in music education, his vision for teaching music composition and his opinion on why acoustic design is so important for music schools. 

In the second part (to be published next week), he shares his experience of visiting the Sistine Chapel, in Rome, where The Sixteen orchestra and a string orchestra played his music. He also shares his experience of attending some famous venues either as a performer or as part of the audience.

Enjoy the read

Marc

 

 

MF: Hi James, first of all, thank you very much for accepting to take time for this interview. Can you introduce yourself?

JMM: My name is James MacMillan, I am a composer, a conductor, a bit of an academic and more recently I formed a little music festival in Ayrshire (Scotland) called the Cumnock Tryst. I am the founder and the artistic director of it.

MF: Can you tell us a little bit more about the Cumnock Tryst?

James MacMillan - Cumnock - Ayrshire
© Marc Marnie 2019

JMM: Yes. I come from Cumnock originally, which is the little village where I grew up. It is in the Eastern part of Ayrshire, to the south of Glasgow. Its background and economic traditions is coal mining, but of course that doesn’t exist anymore. My grandfather was a coal miner, like many men in the area all through the 20th century. During that time he also played music. He was a euphonium player. He played in local brass bands and he sang in his church choir. So, there was an experience of music and a love of music in that community. I remember, it is because of his influence that I wanted to become a musician. He got me my first cornet and took me to my first brass band rehearsals.

Ayrshire is nowadays an area of multiple deprivation. It is not a place where you would expect a high-class arts music festival. So, it raises eyebrows when people see that all this wonderful musical activity is happening there. But it is a place that I remember to be a very musical place and we believe everyone should have access to music, not just those who can afford it. That is part of the ethos that drives what we do.

We bring the great musicians of the world to the Cumnock Tryst. The Sixteen conducted by Harry Christophers, one of the great choirs of the world, has been a few times, the King Singers and the Westminster Cathedral Choir have been. We are working with the Scottish Chamber Orchestra who were going to play this year. We will get them next year.

We have also formed a festival chorus with a lot of local people. This is the on-going project at Cumnock, to bring great music from around the world, to install and continue that musical activity in the area.

With the arrival of the new school [the Barony Campus], our hope is that it will be a catalyst, now that we will have a space to bring larger groups to the town.

MF: So your aspiration for the future is to bring people from different ages and different levels together?

JMM: Yes.

MF: What types of music are performed the Cumnock Tryst?

JMM: All types. Because there has been a strong experience in the area through the generations of choral music, we decided to make choral music quite a regular feature. We get these great choirs coming and we get our chorus singing at their higher level. We have a very wonderful choral director who comes and works with this chorus, and they put on very high standard performances every year.

The British brass band tradition was very strong in the area and it is a tradition that is very much associated with industrial heritage and industrial experience. All the coal mining areas of Scotland and the north of England had high-class brass playing. It is a very particular music culture and we want to feature that with a lot of brass music in the festival.

But we don’t stop there. We realise that chamber music and recitals are very important, so we have some major solo artists who come and play. Steven Osborne, a great pianist, came last year for example. He played Beethoven’s last three piano sonatas as a recital. Nicola Benedetti, who is a patron, (she is from Ayrshire originally and has come a few times), played solo violin (the solo Bach music for example), but also brought a trio and played Ravel, Brahms and so on.

The festival is quite wide-spread and we branch out a lot, we’re bringing a lot of folk musicians from Scotland and elsewhere to perform.

MF: In which venues is the festival organised?

JMM:  We use small venues with very small capacities. Most have three hundred seat capacities, which is fine. The local churches are very good. There is one in particular that has a wonderful acoustic for choral music. People love these venues. There is an attraction about the 19th century churches; they are very beautiful. Some of the local town halls and village halls are also used. Again, they are small with capacities of 180-200 seats.

But we can still have some sort of recitals. Ian Bostridge, a great English tenor, did a recital to an audience of about 180 in the New Cumnock town hall. He had a mixed program of Mahler, Britten and Schubert.

Although we want to maintain the intimacy of these places, we do want to be able to bring orchestras and larger ensembles to the town.

MF: Can you tell us about your involvement and vision in music education?

JMM: Over the years, I have had an oblique relationship with academia. I have had a life in the past of teaching at universities, but because I conduct a lot, in normal circumstances I would be travelling to different parts of the world to perform, so I haven’t been able to maintain regular teaching in conservatoires or Universities.  Although I always want to conserve some link, as it is important for me to have a link with academia.

 

Sir James MacMillan conducting - The Cumnock Tryst
©Cumnock Tryst 2019 Photo: Stuart Armitt

 

I have a visiting professorship at the Royal Conservatoire of Scotland in Glasgow and at the University of St Andrews. I give more of a musicological and theological input in the form of seminars.

Over the last thirty years or so, the British orchestra have been trying to build a new way of working with British schools, which involves not just players but also composers. Instigators are invited into the classrooms to try to encourage composition and creativity, and I have been part of that.

It sometimes involves a freedom in the concept of creativity, there is a lot of improvisation that happens initially. The compositional inspiration can be encouraged by improvising and this is a new way of thinking. It is not a general concept that is accepted worldwide, certainly not in other parts of Europe, and it might be seen as lacking some kind of intellectual discipline.

However, I find it a very useful way not just to engage people with the immediacy of making music, but also to inspire potential composers to think outside the box about how music is made.

I think it can help many types of musicians at different levels of music-making. We have worked with very young children and have tried to make it fun. We have worked with secondary school kids as well as high school kids. We have a project up and running that we are doing through Zoom at the moment, where teenagers are encouraged to write their own music. It has become a major part of what we are doing at the Cumnock Tryst and once we get back to some sort of normality, we will be able to get back into the classroom, doing not just proper improvisations, but actually encouraging them to develop a knowledge of notation. It is not one or the other, it is not free jazz, it is not just free-thinking. It is free to an extent, but we are trying to link it to quite a solid intellectual basis.

We sometimes find there is a divergence of thinking in education. It is either one or the other. Either everything should be free-spirited without reference to the cannon, without reference to the tradition, or the stricter way of thinking is with complete reference to the cannon and everything notated. We are trying to make a melange of the two disciplines. The instincts, the views and the attributes of both can work together. This is a work in progress at the Cumnock Tryst and it seems to be working so far.

MF: How do you find the quality of the music spaces contribute to the musical creativity, the music education and the music performance?

JMM: It is very important for young musicians to sound good in the early stages of their musical development. If they sound good on their instrument, in their voice, in their choir, in their ensemble, to their peers, to their parents and to the local audience that comes to listen, then the delight of music-making is enhanced. And that delight is part of what motivates a young musician to continue.

So, it is vitally important to get the acoustical design right in an educational setting. It should be worked to basics. It should be one of the central considerations in any new build whether it is a school, a community centre or something else. And although we may voice this on the side-lines, we know we don’t have any power, people like myself must continually make up a case for acoustics to be a central educational consideration.

 

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Laboratory or on-site sound insulation rating. Which one to use?

 

You are probably trying to select dry lining products for your project and can see two different ratings on the acoustic specification (or the mark-ups). 

One is Rw, which is a laboratory sound insulation rating. The other is DnT,w , the on-site sound insulation rating. 

 

Note: for ease of reading we will stick to Rw=lab rating and DnT,w= on-site rating. But be aware that the terms can vary depending on the situation including the types of spaces separated by the partition, the type of building and the country. 

 

They both represent the reduction in sound transmission through a building element. In more technical terms, we say they correspond to the airborne sound insulation performance of the element. 

This post explains:

  • which sound insulation rating to use for your selection
  • what both ratings actually mean and what you use them for
  • why, on the acoustic specification, the ratings have different values for a single partition type
  • why some partitions only have a laboratory rating
  • how to remember which one is which without reading this post again

 

Which sound insulation rating to use for your selection?

The quick answer is: use the laboratory rating (Rw).

 

What are the laboratory and on-site sound insulation ratings? and what are they used for?

In practical terms, both ratings represent the difference between the noise levels measured on either side of an element. 

The general principles for the measurements are as follows:

  • generate sound in one room, the source room.
  • measure the sound level in this source room.
  • measure the sound in the room that shares the partition studied, the receiver room. 

 

Sound insulation measurement principles with sound source room, sound receiver room and partition tested for airborne sound insulation
Sound insulation measurement principles

 

Both airborne sound insulation ratings correspond to different types of testing conditions.

The paragraphs below explain this a little bit more.

Laboratory sound insulation rating

The laboratory rating, Rw, is useful for suppliers or manufacturers. This way, they give us an idea of the performances their products can achieve.

In a lab, you test the products in very specific and standardised conditions:

  • The samples tested have a set size and they are connected to specific elements.
  • The testing rooms have particular sizes, shapes and acoustic characteristics. 
  • The performances are measured and calculated in a certain way.

These allow the acoustic consultants to use the laboratory rating as a benchmark for their design. Although they know there is more work to do to achieve what they need.

On-site sound insulation rating

The on-site rating, DnT,w , is given as a requirement in most standards, guidelines and building regulations. 

It represents the sound insulation performance you are contracted to achieve once a building is completed. 

Therefore, this is the sound insulation performance the acoustic engineer will test during the commissioning of a building.

Ok, but why are the ratings different on the acoustic specification?

As mentioned above, the testing conditions in a lab are very particular.

They are designed in a way to minimise the sound transmissions around the samples.

In technical terms, you call it sound flanking. It happens via:

  • the connections
  • the services
  • the flooring systems/slabs
  • the ceiling systems/slabs
  • other paths that connect the building elements

 

sound flanking or sound transmission via the building structure. Sound source room sound receiver room
Sound flanking via the building structure
sound flanking or sound transmission via the building services. Sound source room sound receiver room
Sound flanking via the building services

Acoustic consultants know that the sound flanking is more important in actual buildings than in laboratories. So they underestimate the lab rating by applying a negative correction to take account of the sound flanking. 

This correction is generally around 5-7 dB for drylining partitions. It is less for masonry partitions. 

 

Note: if you are working with “lightweight” partitions that need to achieve ratings with an extension at low frequencies, you might need to use a higher correction. In other words, you need to underestimate even more the laboratory rating.

This is particularly the case for timber constructions.

 

Be aware that, even if you apply this correction, you are not exempt from spending time designing the junction details between the partitions and the other building elements. 

 

And why do some partitions only have one rating?

Because you either won’t have to or won’t be able to test them.

Examples are:

  • partitions with openings, doors, serving hatches or windows/vision panels 
  • service risers
  • lining or boxing systems for services and structural elements
  • lift shafts

 

How to remember which one is which?

Any easy way to remember is to look at the subscripts. 

As described above, both ratings are based on the sound level difference measured between a source room and a receiving room separated by the partition studied.

Rw is the rating measured in a laboratory under standardised conditions, i.e. the same for all the measurements. It can be used as a benchmark and the measurements are weighted. Hence the “w” in the subscript (it corresponds to the way it has been calculated but we won’t go into details here). 

DnT,w is the rating measured on-site under building conditions, i.e. different for most measurements. So as well as weighting the measurements (“w” in the subscript), you also need to standardise them. Hence the “nT” in the subscript.

 

Note: Standardising the measurements takes account of the specific sound reverberation conditions in the receiving room. It gives a more subjective performance for a partition depending on how and where it is installed in a building.

 

So the subscript for the on-site rating is longer than for the laboratory rating, because you need to consider the particular conditions on-site. 

 

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